TO GEOLOGY. 49 



feet. It has a strong resemblance to Petricola pholadiformis 

 (Lamarck) (P.fornicata, Say), but is to appearance entirely 

 without teeth, having several irregular folds about the beak. 

 It differs also in the exterior folds or ribs, which are, in the 

 pholadiformis , marked and situated on the anterior part. 



FAMILY NYMPHACEA. 



GENUS EGERIA. (JVofcfe.) 



Description. Shell subrotund or sub triangular ; margin 

 sometimes crenulate ; hinge variable, sometimes with two 

 lateral teeth ; cardinal teeth two in each valve, diverging, 

 one bifid ; ligament external. 



Observations. Unable to place a considerable group of 

 shells, bearing in the cardinal teeth the same character, 

 in any genus with which I am acquainted, I propose to 

 found a new genus for them, the proper place of which 

 would be between Sanguinolaria and Psammobia. The 

 cardinal teeth have some resemblance to the Lutricola of 

 Blainville, but that able naturalist does not mention a bifid 

 tooth, nor is it so figured in his work. Although there is 

 considerable dissimilarity in the form of the several species 

 of this genus, some being more round and others triangu- 

 lar, the two diverging cardinal teeth, one being bifid, will 

 always be found characteristic of the genus. 



